Abstract <p>This paper investigates water quality changes in the Yangtze River Basin (YRB) following the implementation of the Action Plan for the Protection and Restoration of the Yangtze River. Utilizing monitoring data from 1060 surface water state-controlled sections collected in 2021, we assessed water quality using both single-factor and comprehensive pollution index methods. The results indicate an overall improvement in the basin’s water quality: 94.4% of sites met excellent Class III standards, 4.4% met Class IV, 1.1% met Class V, and only 0.1% were below Class V according to the single-factor evaluation. The comprehensive pollution index showed that 98% of sites were at qualified levels, 1.2% at basically qualified levels, and 0.8% were polluted, with total phosphorus identified as the primary contaminant. Spatial analysis revealed that nitrogen and phosphorus concentrations were higher in rivers and lakes compared to reservoirs, and higher in tributaries than in the main stream. Temporally, dissolved oxygen and ammonia nitrogen levels were lower, while permanganate index and total phosphorus levels were higher during the flood season compared to the non-flood season. The study recommends intensifying total phosphorus pollution control in critical tributaries and regions to further reduce the river’s pollution load.</p>